Speakers for McIntosh pairing??

Got a new (old) 2002 Ford F350 Diesel. Wondering what would be a good speaker set up for this. Don't know if the factory speakers are any good or not (It did have the "premium sound system" from the factory, but haven't heard it yet as the player is busted.)

Have a McIntosh MX401 HU, and a MC420 AMP (4/3/or 2 channel). Understand that as with Home audio, Mac speakers aren't necessarily the best. Wondering about Diamond Audio which I keep hearing a lot about, vs. Dynaudio, or Focal??